1. Field of the Invention
This invention relates to improvements to hydraulic tube benders, and specifically to tube benders which use a center push mandrel to force a tube laterally between two bending dies to create a bend uniform on either side of the mandrel. More specifically, this invention relates to such devices capable of bending very light weight, thin walled tubing, such as titanium tubing used in aircraft.
2. Description of Related Art
Virtually every complex machine and vehicle in today's industrial society employs cylindrical tubing having one or more arcuate bends between end points. When such tubing fails or must be modified, the original bends usually must be replicated as part of the modification or repair. Often it is inconvenient, uneconomic or impossible to return to the original manufacturer for a duplicate or modified tube. Moreover, repair or modification projects often demand immediate substitution of tubes and cannot await research into availability. Considerable interest therefore exists for commonly available tube bending devices capable of bending tubing on demand from models at hand.
Of the devices on the market during recent decades to fill this need, all fall short of the ideal bender. Many cannot bend tubing into angles up to and including one hundred eighty (180.degree.) degrees. Of those that can, most cannot accommodate complex bends in three dimensions, or multiple bends close together on one tube. A need exists for a hydraulic tube bender which can produce complex bends in three dimensions and closely spaced bends on a single tube.
Bending a tube to close tolerances involves careful observation of the bend while it is in progress. Without visual inspection of the contact point of the bending mandrel with the tube, the operator may fail to notice flaws developing in the tube walls, or create an imprecise bend angle. Though bends which fall short of the desired angle may be re-inserted for further bending, a bend which exceeds the desired angle cannot be straitened out without damage to the tube. A need exists for a tube bender which allows direct observation of the tube during bending.
Many tube benders available on the market satisfactorily may bend thick wall tubing such as automobile tail pipes and conduit, but much tighter tolerances and holding pressures are required to bend thin walled tubing such as that used in aircraft. Most benders not specifically designed for thin walled tubing will wrinkle or deform such tubing so that it fails to meet aircraft industry standards. One machine apparently capable of such bends appears in U.S. Pat. No. 5,339,670, issued to Granelli in 1994, but it obviously is bulky, stationary and likely very expensive. A need exists for an inexpensive, easily portable tube bender for thin walled tubing.
A few of the devices in the prior art deserve comment. Hawes (U.S. Pat. Nos. 1,505,887 and 1,530,261) provides portable conduit benders not of the center-push type. The primary shortcoming of such devices is that the precise location of the center of the bend cannot be determined in advance with accuracy. Mingori (U.S. Pat. No. 2,880,779) and Swanson (U.S. Pat. No. 3,018,818) provide center push benders, but rely upon top plates which obscure visibility during the bending operation and prevent closely spaced multiple angles on a single tube. They also rely upon round roller dies which can damage thin walled tubing. Owens (U.S. Pat. No. 5,237,847) also relies on round roller dies and provides a center push die which cannot create 180.degree. bends because of its shape.